fsl_i2c: Use timebase timer functions instead of get_timer()

The current implementation of get_timer() is only really useful after we
have relocated u-boot to memory.  The i2c code is used before that as part
of the SPD DDR setup.

We actually have a bug when using the get_timer() code before relocation
because the .bss hasn't been setup and thus we could be reading/writing
a random location (probably in flash).

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>